surfaceflinger: Only restart zygote if already running.

Bug: 197224273
Test: manual test
Change-Id: I097b78a12dd493fa94b0a8e43cd2844a76c807d6
diff --git a/services/surfaceflinger/surfaceflinger.rc b/services/surfaceflinger/surfaceflinger.rc
index 575e70d..39d7bd9 100644
--- a/services/surfaceflinger/surfaceflinger.rc
+++ b/services/surfaceflinger/surfaceflinger.rc
@@ -3,7 +3,7 @@
     user system
     group graphics drmrpc readproc
     capabilities SYS_NICE
-    onrestart restart zygote
+    onrestart restart --only-if-running zygote
     task_profiles HighPerformance
     socket pdx/system/vr/display/client     stream 0666 system graphics u:object_r:pdx_display_client_endpoint_socket:s0
     socket pdx/system/vr/display/manager    stream 0666 system graphics u:object_r:pdx_display_manager_endpoint_socket:s0